async and await concept

Anil Sharma1983

i am trying to understand async and await concept. so i am make sample program when i run this program take 8 seconds to execute if i execute without async and await it also take 8 second to execute. so what is wrong in this program.

protected async void btnSubmit_Click(object sender, EventArgs e)
{

   Response.Write(DateTime.Now.ToString("dd-MM-yyyy:hh:mm:ss") + " <br/>");

   //dowork();
   await Task.Run(() => dowork());
  // await Task.Run(() => DoAnotherWork());

   DoAnotherWork();
   Response.Write(DateTime.Now.ToString("dd-MM-yyyy:hh:mm:ss") + " <br/>");
   // btnSubmit.Text="Done it";

}

void dowork()
{
Thread.Sleep(5000);
}
void DoAnotherWork()
{
Thread.Sleep(3000);

}

Pete OHanlon

How long would you expect it to complete in? You have 8 seconds worth of operation in there. I assume that you think that dowork will happen at the same time as DoAnotherWork. That's not the way that await operates. It's not, despite what you may think, something that pushes an operation off to another thread and continues processing in that thread - instead, it suspends the operation of the current method until the awaited operation completes. So, you end up with an 8 second delay.

Anil Sharma1983

yes, i was thinking it should completed in 5 seconds. So please clarify to me await and async concept. thanks your help

Pete OHanlon

I just have clarified it for you. The await keyword suspends the method until the task it's waiting on completes, then it moves onto the next operation in the chain. I'm not sure how else I can put this for you.

Anil Sharma1983

thanks Peter for your help

Agent__007

Anil0007 wrote:

i was thinking it should completed in 5 seconds

Well, if you modify your code something like this, it "might" run in 5 seconds..

	 Task t0 = Task.Factory.StartNew(() => dowork());
	 Task t1 = Task.Factory.StartNew(() => DoAnotherWork());
	 
	 await Task.WhenAll(t0, t1);

You have just been Sharapova'd.

F ES Sitecore

Using await doesn't mean your code acts asynchronously. It still behaves as if the code is running synchronously (which is why it takes 8 seconds) but the difference is that when using await the underlying framework means the thread is available to use for other tasks if needed. If you didn't use await and instead just waited for the task to finish then your code would act no differently, but the thread that is waiting for the result can't be used for something else if needed. If you remove the "await" from the dowork then the method will take 3 seconds as dowork will be started on its own task and that will execute asynchronously and then DoAnotherWork will be called which will block for 3s synchronously.

dowork(); // this will block execution for 5s as dowork is executed on the current thread
Task.Run(() => dowork()); // the dowork will happen on its own thread and that thread will run for 5 seconds
// but the code in this block will continue to run so dowork is an asynchronous call
await Task.Run(() => dowork()); // a mix of both the above. The task will still run on its own thread for
// 5 seconds, but execution will wait until that new thread has finished

Richard Deeming

It's not usually recommended to use Task.Run to convert a synchronous method to an async Task, especially if you're going to immediately await that Task: Should I expose asynchronous wrappers for synchronous methods? | Stephen Toub[^] Instead, it's better to push the asynchronous operation down, and make the method your calling return a Task. Also, when you're using async, you should try to avoid Thread.Sleep; use await Task.Delay(...) instead: Visual C#: Thread.Sleep vs. Task.Delay[^] And as Agent__007 said, if you want both methods to run in parallel, you need to use Task.WhenAll to wait for them.

protected async void btnSubmit_Click(object sender, EventArgs e)
{
Response.Write(DateTime.Now.ToString("dd-MM-yyyy:hh:mm:ss") + " <br/>");

Task first = dowork();
Task second = DoAnotherWork();
await Task.WhenAll(first, second);

Response.Write(DateTime.Now.ToString("dd-MM-yyyy:hh:mm:ss") + " <br/>");

}

async Task dowork()
{
await Task.Delay(5000);
}

async Task DoAnotherWork()
{
await Task.Delay(3000);
}

Since you're using ASP.NET WebForms, you should consider using the RegisterAsyncTask method[^] to run your async code, and avoid using async void where possible: Using Asynchronous Methods in ASP.NET 4.5[^]